Mitsubishi Electric MSC-GE-VB Service Manual page 7

4. High pressure protection (MUH-GD80VB, MUH-GE50VB)
During heating operation, the outdoor fan and the compressor are controlled by the temperature of indoor coil thermistor
for excess rise protection of compressor discharge pressure.
• Outdoor fan
When the temperature of indoor coil thermistor goes to 55°C or more, the outdoor fan is turned OFF.
When the temperature of indoor coil thermistor becomes 52°C or less, the outdoor fan is turned ON.
• Compressor
When the temperature of indoor coil thermistor goes to 75°C or more, the compressor is turned OFF.
3 minutes after the compressor is turned OFF and if the temperature of indoor coil thermistor becomes 75°C or less, the
compressor is turned ON.
NOTE: During the high pressure protection and for 10 seconds after high pressure protection, defrosting of outdoor heat
exchanger is not detected by the defrost thermistor.
5. Defrosting
Defrosting of outdoor heat exchanger is controlled by deicer P.C. board, with detection by the defrost thermistor.
(1) Starting conditions of defrost
When all conditions of a) ~ c) are satisfied, the defrosting operation starts.
a) Under the heat operation, the compressor cumulative operation time exceeds 40 minutes without the defrosting opera-
tion working.
b) The defrost thermistor reads -3°C or less.
c) After releasing the high pressure protection 4 minutes and 10 seconds have elapsed.
(2) Releasing conditions of defrost
When the condition d) or e) is satisfied, the defrosting operation stops.
d) The defrost thermistor reads 10°C (MUH-GE50VB) /13°C or more (MUH-GD80VB).
e) The defrosting time exceeds 10 minutes.
(3) Defrosting time chart
Defrost thermistor
13°C or more (MUH-GD80VB)
10°C or more (MUH-GE50VB)
-3°C or less
Outdoor 52C
ON
contactor
(Compressor)
OFF
ON
X62
(R.V. coil)
OFF
ON
SR61
Outdoor fan
OFF
ON
Defrost
counter
OFF
ON
Indoor fan
Very Low
OFF
Horizontal
Indoor vane
Set position
NOTE: • When the indoor coil thermistor reads above 18°C, indoor fan operates at Very Low for 30 seconds.
• When the indoor coil thermistor reads 18°C or less, the indoor fan stops.
15 seconds
30 seconds
Maximum 10 minutes
NOTE
30 seconds
7
5 seconds